Processes are known for the production of hydrogen by means of a series of chemical reactions. For example, hydrogen has been prepared in a chemical system which includes the reaction of mercury with hydrogen bromide, with the resulting formation of mercury bromide and hydrogen. Hydrogen has also been prepared by the hydrolysis of boron hydrides, such as sodium borohydride. Other processes have also been described in the prior art literature. However, the prior art processes for the most part are subject to one or more disadvantages or difficulties, such as corrosiveness, instability or toxicity of the materials involved, high temperature or difficult separations required in carrying out the prior art processes, all of which militate against their commercial feasibility.
The process of the invention in its preferred embodiment uses cadmium in reaction with steam to produce hydrogen. This preferred embodiment actually uses gallium triiodide, (GaI.sub.3), which disassociates at elevated temperatures to absorb a large fraction of the heat required to split the water into hydrogen and oxygen. Iodine is used to form cadmium iodide and cadmium iodate at relatively low temperatures, in order to recover the cadmium for re-use. Decomposition of the cadmium iodate is achieved at elevated temperatures, for example, by use of heat from nuclear fission. An advantage of this embodiment is the non-corrosiveness and the ready separation of the cadmium during the recovery process.
Another embodiment of the process uses nickel to produce hydrogen. This embodiment also has the advantage in that nickel is non-corrosive, and it combines with steam under pressure at relatively low temperature to produce hydrogen and nickel hydroxide, Ni(OH).sub.2, with minimum heat requirements. The nickel is subsequently recovered for re-use by heating the hydroxide to form the oxide NiO, and the reaction of nickel oxide with iodine to form nickel iodide, NiI.sub.2 and nickel iodate Ni(IO.sub.3).sub.2, which are also produced at relatively low temperatures, although pressure is required. The nickel iodate is then decomposed at elevated temperatures to release the oxygen and recover nickel oxide and iodine for re-use. The nickel iodide is either decomposed directly with heat or reacted with carbon monoxide under pressure to form nickel carbonyl, Ni(CO).sub.4, which is decomposed at relatively low temperatures by adding heat.
Thus, the invention provides an improved, low cost process for producing hydrogen from water by the addition of heat to a series of chemical reactions. The equipment to produce the hydrogen by the process of the invention requires only the input of water and heat to produce an output of hydrogen gas. The substances used in the reaction are recycled so that no additional substances are required. The operation of the equipment is analogous to that of an electrolytic cell, except that heat is applied instead of electricity. By using heat directly in the practice of the process of the present invention, instead of going through an intermediate step of converting the heat into electricity, hydrogen can be produced with less energy than is required by electrolysis.
The process of the present invention fulfills the criteria of providing a phase change at each step to aid separation; of using relatively non-corrosive substances to prevent contamination from the equipment; and of using reactions that absorb heat at relatively low temperature.
The use of cadmium or nickel in the embodiments of the process to be described is advantageous because the equipment can be made to present a surface of the same metal, and in this way, any reaction with the equipment surface will not contaminate the process.